In general, plastic films so strongly tend to be statically charged that their use may be greatly restricted in many instances. For example, in the case of light-sensitive silver halide photographic materials, supports made of polyester are commonly used, which tend to be statically charged particularly under conditions of low humidity as in the winter. It is particularly important to take a measure for antistatic, when in recent years high-speed photographic emulsions are coated at a high speed or light-sensitive materials with high sensitivity are exposed to light through automatic printers.
Once a light-sensitive material has been statically charged, static marks may occur because of release of the stored energy, or foreign matters such as dust may be attracted to cause occurrence of pin holes, resulting in a serious deterioration of product quality. Its restoration brings about a great lowering of workability.
Methods of preventing plastic films from being statically charged can be exemplified by a method in which an anionic compound such as an organic sulfonate or an organic phosphate is incorporated, a method in which a metal compound is deposited, and a method in which an anionic compound, a cationic compound or what is called conductive particles are coated. The method in which an anionic compound is incorporated in plastic films enables inexpensive manufacture, but can not achieve a sufficient antistatic effect. It also requires use of a low-molecular compound as a compound usable together with the anionic compound. Hence this method has the problems that the adhesion between a film and a layer formed thereon in a laminate may be lowered because of blooming, the film has no water resistance, and the compound may be transferred to the film. The method in which a metal compound is deposited to the films can achieve superior antistatic properties, and in recent years has come into wide use for providing transparent conductive films. This method, however, has a problem of a high production cost.
The method in which conductive carbon or conductive metal particles are coated can bring about relatively good results and low coast, but may cause a deterioration of transparency of films.
Under such circumstances, it is common to use a method in which an anionic compound or a cationic compound is coated on a plastic film.
For example, in light-sensitive materials, fluorine-containing surface active agents, cationic surface active agents, amphoteric surface active agents, surface active agents or polymeric compounds containing a polyethylene oxide group, polymers having a sulfonic acid or phosphoric acid group in the molecule, and so forth have been recently used as antistatic agents.
In particular, methods of adjusting triboelectric series by the use of fluorine-containing surface active agents or improving conductivity by the use of conductive polymers have been widely used. For example, Japanese Patent Publications Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication(s)) No. 91165/1974 and No. 121523/1974 disclose an example in which an ion type polymer having a dissociative group in the main polymer chain is used.
In these conventional methods, however, antistatic properties may be greatly deteriorated when developing is carried out. This is presumed to be due to a loss of antistatic properties as a result of the processing carried out through the steps such as developing using an alkali, fixing in an acidic environment, and washing. Hence, problems may arise such that pinholes are produced because of adhesion of dust in such an instance in which a film having been processed is further brought to printing as in the case of printing light-sensitive materials.
Taking account of such problems, Japanese Patent O.P.I. Publications No. 84658/1980 and No. I74542/1986 propose to provide an antistatic layer comprising i) a hydrophobic polymer containing a carboxyl group and ii) a polyfunctional aziridine. This method makes it possible to retain antistatic properties even after the processing. This antistatic layer, however, may cause the problem that an adhesion between a plastic film, e.g., a polyester film, and a hydrophilic colloid layer such as the antistatic layer formed thereon by coating is so poor that peel-off or delamination occurs during the processing in an aqueous solution, e.g., a developing solution as in the case of the processing of light-sensitive materials.